Method for electrodepositing nickel-iron alloys



July 21, 1964 F. H. EDELMAN 3,141,337

METHOD FOR ELECTRODEPOSITING NICKEL-IRON ALLOYS Filed Nov. 28, 1961 3 Sheets-Sheet 1 United States Patent 3,141,837 METHOD FOR ELECTRODEPOSITING NICKEL-IRON ALLOYS Frank H. Edelman, Yardley, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Nov. 28, 1961, Ser. No. 155,301 9 Claims. (Cl. 204-43) This invention relates to a method for electrodepositing nickel-iron alloys in which the composition and magnetic properties of the deposit may be intermittently or continuously adjusted during the process.

Because nickel-iron alloys, particularly permalloy, are magnetic and exhibit a square magnetic hysteresis characteristic, they are a desirable component for magnetic memories and other data processing equipment. Such alloys have been made previously by electrodeposition from an aqueous electrolyte. The previous processes maintain constant either the plating current (current between anode and cathode) or the plating voltage (voltage between anode and cathode). By such previous processes, the composition, and therefore the magnetic properties, of the deposit vary with time as the electrodeposition proceeds. Such previous processes seek to control the composition and the magnetic properties of the deposit by a careful selection and control of the electrolyte composition and current density, and by a careful control of the electrolyte temperature. These controls are only partially successful because each electrolyte composition is used for only one particular alloy composition, and because the electrolyte composition varies with time as the electrodeposition proceeds.

An object of this invention is to provide an improved method for electrodepositing nickel-iron alloys.

A further object is to provide a method for electrodepositing nickel-iron alloys wherein the composition of the alloy may be intermittently or continuously controlled during the period of deposition.

Another object is to provide a method for electrodepositing nickel-iron alloys of substantially uniform composition.

In the method of the invention for depositing nickeliron alloys, an anode, a cathode, and a reference electrode are immersed in an aqueous electrolyte containing nickel and iron salts. A direct current plating voltage is applied across the anode and the cathode and a plating current passes through the electrolyte whereby the alloy deposits upon the cathode. During the course of deposition, the voltage between the cathode and the reference electrode, referred to as the operating plating control voltage V is detected and compared with a preselected applied plating control voltage V The difference or error plating control voltage V is applied to adjust the plating voltage to provide a preselected, compositional distribution in the deposited alloy. Where a substantially uniform composition is desired the operating plating control voltage V is maintained substantially constant throughout the deposition. Where a particular compositional distribution is desired, the operating plating control voltage V is adjusted during electrodeposition according to a preselected program. In the process of the invention, both the plating current and the plating voltage are permitted to vary.

The cathode potential is the primary factor in determining the reaction rates for the electrodeposition of both the nickel and the iron. By controlling the cathode potential With respect to some constant reference voltage (or operating plating control voltage V the reaction rates of each constituent of the deposit (and therefore the composition of the deposit) are controlled simultaneously. The method of the invention has 3,141,837 Patented July 21, 1964 the further advantage that it may derive a low voltage control signal at any time during the process which may be intermittently or continuously applied to adjust the composition of the deposit as a correction or a preselected program.

In one particular embodiment of the invention, a magnetic characteristic of the deposited alloy is sensed during the electrodeposition. The sensed characteristic is converted to an operating magnetic control voltage V which is then used to adjust the operating plating control voltage V to provide the desired magnetic characteristic in the deposited alloy. In any of the embodiments of the invention, a magnetic field may be applied to the cathode during the electrodeposition to orient the deposit so as to optimize the magnetic property of the deposit.

A detailed description of the invention appears below to be read in conjunction with the drawings in which:

FIGURE 1 is a partially-schematic, partially-sectional view of a first apparatus for practicing the method of the invention,

FIGURE 2 is a graph comparing the iron content of the deposited alloy versus the thickness of the deposit obtained using the method of the invention,

FIGURE 3 is a graph comparing the iron content of the deposited alloy versus the cathode potential in the method of the invention,

FIGURE 4 is a partially-schematic, partially-sectional view of a second apparatus for practicing the invention which includes a solenoid for magnetically orienting the deposited alloy, and means for rotating the sample during electrodeposition, and

FIGURE 5 is a partially-schematic, partially-sectional view of a third apparatus for practicing the invention which includes means for monitoring the magnetic hysteretic characteristic of the alloy during electrodeposition.

Similar reference characters are used for similar structures throughout the drawings.

FIGURE 1 illustrates a particular apparatus for practicing the invention. The particular apparatus comprises a tank 21 holding a quantity of electrolyte 23. The composition of the electrolyte is described in detail below. An anode 25 comprising a cylindrical wire gauze of platinum metal is submerged in the electrolyte 23. The anode 25 is open at its ends and the ends are positioned one to face upwards toward the surface of the electrolyte 23 and one to face downwards toward the bottom of the tank 21. The anode 25 may be of any geometric shape and may be solid or porous or of gauze. Where the electrolyte 23 contains all of the material to be electrodeposited, the anode may be of any convenient non reactive material, such as stainless steel, carbon, of platinum. Platinum is preferred. Optionally, according to electroplating practice, the anode 25 may be of a nickeliron alloy or nickel and it may provide a source of part of the material to be electrodeposited.

A cathode 27 is immersed in the electrolyte 23 Within the cylindrical gauze 25. As illustrated in FIGURE 1, the cathode 27 comprises an inert substrate 29 which has a metallized surface region 31. The preferred inert substrates are smooth-surfaced, amorphous, and nonconducting. Glass or plastic are convenient for this purpose. The surface of the substrate may be metallized, for example, by evaporating one or a combination of metals upon the surface thereof. Optionally, a solid metallic substrate may be used. It is important when using a solid metal cathode that it be polished or otherwise treated to present a smooth surface for receiving the electrodeposit.

A permanent magnet 33 is positioned around the tank 21 to provide an orienting magnetic field to the alloy which will be electrodeposited on the metallized surface 31. As illustrated in FIGURE 1, the magnet 33 is of the permanent type. The orienting magnetic field is pref erably applied to the metallized surface 31 in a direction which is parallel to the surface thereof. Any other means for applying an orienting magnetic field parallel to the surface which will receive the electrodeposit may be used for example, a Helmholtz coil may be used, or a solenoid may be used.

The power for electrodepositing the alloy is supplied from a power supply 35 as indicated by the dotted rectangle in FIGURE 1. In this embodiment, 115 volts at 60 cycles is applied to the terminals designated AA. This power is fed to an auto transformer 37 which adjusts the input voltage to a desired value, by adjustment of a contact 35. The electric power is next passed through a power transformer 41 where the input voltage is reduced and the current increased. The transformed current is then passed through the rectifier and filter 43, where the power is converted to direct current. The plating circuit comprises the rectifier and filter 43. The rectifier is connected from a terminal of positive polarity to the anode 25 by a lead 45; and. from the negative terminal through a lead 46, then through an integrator 49 and a lead 47 to the cathode 27. The integrator 49 provides a summation of the number of coulombs or f-aradays passed through a plating circuit to indicate the amount of alloy which has been electrodeposited. This is a measure of the thickness of the deposit. The plating circuit applies a plating voltage V between anode 25 and the cathode 27, and passes a plating current 1 through the circuit.

A reference electrode 51 is also immersed in the electrolyte 23 within the anode 25 and opposite the cathode 27. The position of the reference electrode 51 may be varied in that it may be placed outside the cylindrical anode, and may be spaced at any convenient distance from the cathode 27. Preferably, the reference electrode 51 should be positioned as close as possible to the cathode 27. The reference electrode 51 may be any standard half cell which produces a known and constant voltage in the electrolyte 23. A preferred reference electrode is a calomel electrode.

A control circuit indicated by the dotted rectangle 53 comprises a battery or other DC. power source 55 connected in series with a variable resistor 57 and a potentiometer 59. A voltmeter 61 is connected across the potentiometer 59. The most positive terminal of the resistor of the potentiometer 59 is connected to the reference electrode 51 through a lead 63. The movable tap of the potentiometer is connected to a servo amplifier 65 with a lead 67. The variable resistor 57 is provided so that the voltage applied to the potentiometer 59 may be adjusted to a desired value as read on the voltmeter 61. The output of the control circuit 53 is an applied plating control voltage V which is applied between the reference electrode 51 and the servo amplifier 65. The other input of the servo amplifier is received from a lead 69 connected directly to the lead 47. A gear train 73 is connected to the movable tap 30 of the auto transformer. A motor 71, under control of the servo amplifier 65 drives the gear train 73.

In operation, the polarities of the cathode 27, the reference electrode 51, and the battery 55 are arranged so that the applied plating control voltage V is compared to the o erating plating control voltage V between the reference electrode 51 and the cathode 27. The difference V ,V is an error plating control voltage V across the input to the servo amplifier. This error plating con trol voltage is amplified in the servo amplifier 65 and is used to drive the motor 71 which adjusts the contact 39 on the autotransformer 37 through the gear train 73 and mechanical link-ages 72 and 74 in a direction tending to reduce the error voltage.

To operate the foregoing apparatus, the electrolyte 23, which is also called the plating bath, is first prepared and placed in the tank 21. The electrolyte is typically an aqueous solution of iron and nickel sulfates with boric acid as a buffer. Other agents to lower the interfacial tension, reduce stress, increase conductivity, and decrease ionization may be added if desired. Anions which may be used are sulfates, chlorides, acetates, sulfamates and pyrophosphates. However, when changing the anion, an adjustment is made in the pH of the electrolyte and the cathode potential to achieve optimum results. A typical electrolyte comprises in grams per liter of Water:

Nickel sulfate 218 Sodium chloride 0-15 Boric acid 15 to 30 Sodium lauryl sulfate 0.1 to 0.5 Saccharin 0.4 to 20 Ferrous ammonium sulfate 8 to 138 The range of iron content, as metal, in the electrolyte is from 2 to 25 weight percent of the total iron plus nickel present in the electrolyte. Thus, the weight ratio of Ni/Fe in the electrolyte is between 75/25 and 98/2. The bath is operated at a pH between 1.5 and 3.5. A pH of about 2.5 is preferred. The lower the pH, the more hydrogen is evolved; While the higher the pH, the less stable is the ferrous ion. The electrolyte is maintained at a temperature of about 50 C. and, preferably, some form of stirring or agitating the electrolyte is provided. An operating temperature of 50 C. provides uniformity of results, but is not considered to be critical. Equivalent magnetic data is obtained with alloys which have been electrodeposited at lower temperatures. Stirring the electrolyte promotes reproducibility of results, but suitable alloys can be electrodeposited without stirring, depending upon the geometry of the cathode, the anode and the electrolytic cell. Stirring may be achieved, for eX- ample, by rotating the cathode 27 or with a mechanical stirrer to circulate the electrolyte 23 around the cathode 27.

After the electrolyte 23 is placed in the tank 21, the anode 25, the cathode 27, the magnet 33, and the reference electrode 51 are positioned in the electrolyte 23. The variable resistor 57 is adjusted to provide the maximum desired applied plating control voltage, Which is read on the volt meter 61. The potentiometer 59 is then adjusted to provide the desired value of the applied plating control voltage V The plating voltage V is now applied and the electrodeposition commences. As the electrodeposition continues, the plating voltage V will tend to vary and therefore the operating plating control voltage V will also tend to change. As V changes, an error plating control voltage V appears across the input of the servo amplifier 65. This error plating control voltage V is used to start the motor 71 which readjusts the contact 39 on the autotransformer 37 to maintain the operating plating control voltage V either substantially constant or according to a programmed value. When the operating plating control voltage V is maintained substantially: constant, the composition of the electrodeposited alloy remains substantially constant. When the operating plating control voltage V is programmed, the composition of the electrodeposited alloy may be varied in composition as desired. The iron content in the electrodeposit is usually different than the iron content in the electrolyte. The iron content in the electrodeposit is usually between 10 and 50 weight percent of the total iron and nickel present. Thus the weight ratio of Ni/Fe in the electrodeposit is usually between 50/50 and 10.

The applied plating control voltage V at which the potentiometer 59 is set is varied according to the iron content in the electrolyte 23, the current density required, and the desired composition of the electrodeposited alloy. These parameters are determined empirically. For an iron content in the electrolyte varying between 2 and 25 weight percent of the total of iron and nickel. The electrolyte may be made up in accordance with the specific FIGURE 2 is a graph showing the relationship of iron content in percent of the electrodeposited alloy plotted against the thickness of the electrodeposited alloy, by operating the apparatus of FIGURE 1 with a constant value of operating plating control voltage V It will be noted that the proportion of iron in the deposit remains substantially constant with thickness, which implies also that the proportion of iron in the deposit remains substantially constant with time of electrodeposition.

FIGURE 3 is a graph comparing the percentage of iron content of the electrodeposited alloy against the operating plating control voltage V It will be noted that at about 600 millivolts, the iron content of the electrodeposited alloy is about 20 percent. As the operating plating control voltage V increases from 600 millivolts, the iron content of the electrodeposited alloy decreases to about 8 percent at an applied voltage of about 1400 millivolts. With this curve, therefore, one may preselect the iron content of the electrodeposited alloy by a proper selection of the operating plating control voltage V And, the iron content of the electrodeposited alloy may be programmed as desired by a suitable program of applied plating control voltage during the electrodeposition.

Example 1 An apparatus of FIGURE 1 is operated as follows. An electrolyte of the following composition in grams per liter of water is placed in the tank 21:

Nickel sulfate 218 Sodium chloride 9.7 Boric acid 25 Sodium lauryl sulfate 0.2 Saccharin 0.82 Ferrous ammonium sulfate 19.0

The electrolyte is adjusted to a pH of 2.5 and a temperature of about 50 C. An applied voltage V of 780 millivolts is applied, and the alloy is electrodeposited on the cathode 27 with a plating current of about 30 milliamperes. Maintaining the operating plating control voltage V constant, the composition of the electrodeposited alloy is substantially constant at 12.6 weight percent.

FIGURE 4 illustrates a second plating apparatus which may be used to practice the invention. The power source 35 and the control circuit 53 are the same as in FIGURE 1. The tank 21 is filled with an electrolyte 23 as described in FIGURE 1. A cylindrical gauze anode 25 is immersed in the electrolyte 23. A cathode 27 comprising a substrate 29 having a metallized portion 31 is inserted in a holder '75. The holder is mounted on a shaft 77 which is connected to a motor 79. The motor 79, shaft 77 and holder 75 are so mounted so that the cathode 27 may be rotated in the electrolyte 23 within the anode 25. A reference electrode 51 is also immersed in the electrolyte 23 but outside the cylindrical anode 25. A solenoid 81 surrounds the tank 21 and has a source of alternating or direct current connected to leads X-X. The solenoid 81 is positioned to provide an orienting magnetic field parallel to the surface of the metallized portion 31. In operation, the orienting magnetic field is applied, an operating plating control voltage V is produced between the reference electrode 51 (through the lead 63) and the cathode 27 (through shaft 77, a commutator brush 83, and lead 69). The operation of the apparatus of FIGURE 4 is then the same as the operation of the apparatus of FIGURE 1 except that the cathode rotates during the operation of the device. A typical operation of the apparatus of FIGURE 4 is now given in Example 2.

Example 2 A substrate 29 about 1.8 centimeter square of glass 29 is provided for cathode 27. A conducting surface 31 is applied by first evaporating and depositing a layer of chromium metal about 350 AU. thick on the substrate 29 followed by evaporating and depositing a second layer of gold metal about 2,000 AJU. thick to make the cathode 27. The anode is a 1.5 inch diameter platinum gauze cylinder encircling the cathode 27. The cathode 27 is rotated at about 200 rpm. Using an applied plating control voltage V (and V of 600 millivolts, a plating current I of about 18 milliamperes, and maintaining the operating plating control voltage V constant, an electrodeposit is obtained having a uniform iron content of about 20.5 percent.

FIGURE 5 illustrates a third apparatus for practicing the invention which includes means for monitoring the magnetic hysteretic property of the electrodeposited alloy. The tank 21, the electrolyte 23, and the reference electrode 51 are the same as described for FIGURE 1. A cathode 27, which comprises an insulating substrate 29 having a conducting region 31, is mounted in a holder 85. The holder also has a small sense coil 87 mounted opposite the surface 31. The sense coil 87 comprises 3000 turns of No. 40 gauge copper wire. The cathode assembly is stationary and the electrolyte 23 is circulated within the anode 25 by a mechanical circulator (not shown).

The circuits are the same as those in FIGURE 1 except as follows: A pair of drive coils 91 are positioned on opposite sides of the cathode 27 and outside the tank 21. Each drive coil 91 comprises a solenoid of about 11 inches mean diameter and made of 81 turns of No. 16 gauge copper wire. The two drive coils 91 are connected electrically in series with an interconnection 93. A pair of drive coil connections 95 connect the drive coils 91 to a source of drive power 97. In this embodiment, the drive power is 115 volts and 420 cycles per second. The drive coils 91 are positioned around the tank 21 so that the drive magnetic fields produced therefrom are additive and are in a direction parallel to the surface of the conducting region 31 of the cathode 27. As viewed in FIG- URE 5 this may be, for example, in a direction either into or out of the plane of the paper.

A pair of sense coil connections 89 connect the sense coil 87 to an integrator 99. The integrator 99 is an RC network which converts the voltage output of the sense coil 87 (which is a measure of d/dt, where 4) is the flux induced in the sense coil and t is time) to an integrated voltage (which is a measure of p independent of time).

The integrated voltage is also amplified in the integrator 99 and fed to a converter 103 through leads 101. The converter 103 converts the integrated voltage to an operating magnetic control voltage V which is a function of the coercive force H of the electrodeposited film. The operating magnetic control voltage V. is fed through leads 105 to a comparator 107 where it is compared against preselected applied magnetic control voltage V from a voltage source 109 through leads 111. The difference or error voltage V is fed through leads 113 to an amplifier and servo mechanism 115, which operates a mechanical linkage 117 to readjust the potentiometer 59.

The apparatus of FIGURE 5 is operated as described for the apparatus of FIGURE 1. In addition, after the electrodeposition has started, a drive current is applied to the connections 95, for example 115 volts and 420 cycles per second, from the voltage source 97, to alternately magnetize and demagnetize the electrodeposited alloy during the plating process. Changes in induced magnetic flux in the electrodeposited alloys that link the coil 87 are sensed by the sense coil 87, where they are converted to a voltage which appears across the sense coil connections 89. This sensing may be carried on continuously or intermittently during electroplating.

In practice, it has been found convenient to include a bucking coil (not shown) to cancel out the induced signal in the sense coil under conditions where no test sample is present. In one embodiment, the bucking coil has the same number of turns as the sense coil 87. The bucking coil is connected in series with the sense coil 87 and is positioned adjacent thereto.

The output of the sense coil 87 is a voltage which is a measure of dgb/dl. This voltage is integrated and amplified in the integrator 99, converted to an operating magnetic control voltage V and then compared with an applied magnetic control voltage V which represents a desired value of H Any difference between the two produces an error magnetic control voltage V which is used to correct the value of V to reduce the difference to zero. The applied magnetic control voltage V may be a fixed value or may be varied in a preselected program.

The hysteresis loop of electrodeposited film may be monitored and displayed during the electrodeposition on an oscilloscope 119 of a cathode ray tube display 121. For this purpose, the integrated voltage from the integrator 99 is fed through leads 123 and 133 to the vertical input 125 of the oscilloscope 119. The drive voltage is fed through a lead 127 to the vertical input 125 of the oscilloscope. The drive voltage is also fed through a lead 129 to a shear compensator 131. The shear compensator 131 is also fed the integrated voltage through a lead 133 from the integrator 99. The shear compensator 131 compensates for the shear in the hysteresis loop as the electrodeposited film becomes thicker. The output of the shear compensator 131 is applied through a lead 137 to the horizontal input 135 of the oscilloscope 119. The hysteresis loop is displayed on the display 121.

What is claimed is:

1. A method for electrodepositing a nickel-iron alloy which comprises immersing a cathode in an aqueous electrolyte comprising soluble salts of nickel and iron, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an electrical signal and applying said electrical signal to adjust the voltage between said anode and said reference electrode to provide a preselected distribution of magnetic property in said deposited alloy.

2. A method for electrodepositing a nickel-iron alloy wherein the weight ratio of Ni/Fe is between 50/50 and 90/10 which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an electrical signal and then applying said electrical signal to adjust the voltage between said cathode and said reference electrode to provide a preselected distribution of said magnetic property in said deposited alloy.

3. A method for electrodepositing a nickel-iron alloy wherein the weight ratio of Ni/Fe is between 50/50 and 90/10 which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron wherein the weight ratio of Ni/Fe is between 75/25 and 98/2, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy upon said cathode, applying an orienting magnetic field to said alloy during the deposition thereof, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an electrical signal voltage, comparing said electrical signal voltage with a known voltage to provide a differential voltage and then applying said differential voltage to adjust the voltage between said cathode and said reference electrode to provide a pre- 8 determined distribution of magnetic property in said deposited alloy.

4. A method for electrodepositing a nickel-iron alloy film of substantially uniform composition which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron wherein the weight ratio of Ni/Fe in said electrolyte is between 75/ 25 and 98/ 2, said cathode comprising an electrically-insulating support having an electrically-conducting surface region thereon, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy film upon said cathode, sensing the magnetic hysteresis characteristic of said deposited alloy, converting said sensed magnetic characteristic to an operating magnetic control voltage, providing a preselected applied magnetic control voltage, deriving an error plating control voltage which is the differential between said operating magnetic control voltage and said applied magnetic control voltage and then applying said error magnetic control voltage to adjust the voltage between said cathode and said reference electrode to provide a substantially uniform magnetic property through said deposited alloy film.

5. A method for electrodepositing a nickel-iron alloy film of substantially uniform composition which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron and said cathode comprising a glass support having an electrically conducting surface region thereon produced by first depositing a layer of chromium metal on a surface of said support and then depositing a layer of gold metal upon said chromium layer, immersing an anode in said electrolyte, said anode comprising a cylindrical gauze of platinum metal encircling said cathode, immersing a constant voltage calomel reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy film upon said cathode, sensing the magnetic hysteresis characteristic of said deposited alloy, converting said sensed magnetic property to an operating magnetic control voltage providing a preselected applied magnetic control voltage, deriving an error plating control voltage which is the differential between said operating magnetic control voltage and said applied magnetic control voltage and then applying said error magnetic control voltage to adjust the voltage between said cathode and said reference electrode to provide a substantially uniform magnetic property through said deposited alloy film.

6. A method for electrodepositing a magnetic nickeliron alloy which comprises immersing a cathode in an aqueous electrolyte comprising soluble salts of nickel and iron, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an operating magnetic control voltage, providing a preselected applied magnetic control voltage, deriving an error magnetic control voltage which is the differential between said operating magnetic control voltage and said preselected applied magnetic control voltage, detecting the operating plating control voltage between said reference electrode and said cathode, providing a preselected applied plating control voltage, deriving an error plating control Voltage which 'is the differential between said operating plating control voltage and said preselected applied plating control voltage, applying said error magnetic control voltage to adjust said applied plating control voltage, and applying said adjusted error plating control voltage to adjust said operating plating control voltage, to provide a predetermined distribution of magnetic property in said deposited alloy.

7. A method for electrodepositing a magnetic nickeliron alloy wherein the weight ratio of Ni/Fe is between 50/50 and 90/10 which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an operating magnetic control voltage, providing a preselected applied magnetic control voltage, deriving an error magnetic control voltage which is the differential between said operating magnetic control voltage and said preselected applied magnetic control voltage, detecting the operating plating control voltage between said reference electrode and said cathode, providing a preselected applied plating control voltage, deriving an error plating control voltage which is the differential between said operating plating control voltage and said preselected applied plating control voltage, applying said error magnetic control voltage to adjust said error plating control voltage, and applying said adjusted error plating control voltage to adjust said operating plating control voltage to provide a predetermined distribution of magnetic property in said deposited alloy.

8. A method for electrodepositing a magnetic nickeliron alloy wherein the weight ratio of Ni/ Fe is between 50/50 and 90/10 which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron wherein the weight ratio of Ni/Fe is between 75/25 and 98/2, immersing an anode in said electrolyte, immersing a reference electrode in said electrolyte, passing a direct current through said electrode between said anode and said cathode to deposit said alloy upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting the sensed magnetic property to an operating magnetic control voltage, providing a preselected applied magnetic control voltage, deriving an error magnetic control voltage which is the differential between said operating magnetic control voltage and said preselected applied magnetic control voltage, detecting the operating plating control voltage between said reference electrode and said cathode, providing a preselected applied plating control voltage, deriving an error plating control voltage which is the differential between said operating plating control voltage and said preselected applied plating control voltage, applying said error magnetic control voltage to adjust said error plating control voltage, and applying said adjusted error plating control voltage to adujst said operating plating control voltage to provide a predetermined distribution of magnetic property in said deposited alloy.

9. A method for electrodepositing a nickel-iron alloy film of substantially uniform composition which comprises immersing a cathode in an aqueous electrolyte, said electrolyte comprising soluble salts of nickel and iron wherein the weight ratio of Ni/ Fe is between 25 and 98/2, said cathode comprising a glass support having an electrically conducting surface region thereon, immersing an anode in said electrolyte, said anode consisting essentially of platinum metal, immersing a reference electrode in said electrolyte, passing a direct current through said electrolyte between said anode and said cathode to deposit said alloy film upon said cathode, sensing the magnetic hysteresis of said deposited alloy, converting said sensed magnetic property to an operating magnetic control voltage, providing a preselected applied magnetic control voltage, deriving an error magnetic control voltage which is the differential between said operating magnetic control voltage and said preselected applied magnetic control voltage, detecting the operating plating control voltage between said reference electrode and said cathode, providing a preselected applied plating control voltage, deriving an error plating control voltage which is the differential between said operating plating control voltage and said preselected applied plating control voltage, applying said error magnetic control voltage to adjust said applied plating control voltage, and applying said adjusted error plating control voltage to adjust said operating plating control voltage, to provide a uniform magnetic property through said deposited alloy film.

References Cited in the file of this patent UNITED STATES PATENTS 2,584,816 Sands Feb. 5, 1942 2,989,446 Hammond June 20, 1961 3,047,423 Eggenberger et al July 31, 1962 3,047,475 Hespenheide July 31, 1962 FOREIGN PATENTS 623,795 Canada July 11, 1961 OTHER REFERENCES Glasstone et al.: Transactions of the Faraday Society, vol. 23, 1927, pages 213226.

Potter: Electro Chemistry, Cleaver Hume Press Ltd., London, 1956 (pages 299-301). 

1. A METHOD FOR ELECTRODEPOSITING A NICKEL-IRON ALLOY WHICH COMPRISES IMMERSING A CATHODE IN AN AQUEOUS ELECTROLYTE COMPRISING SOLUBLE SALTS OF NICKEL AND IRON, IMMERSING AN ANODE IN SAID ELECTROLYTE, IMMERSING A REFERENCE ELECTRODE IN SAID ELECTROLYTE, PASSING A DIRECT CURRENT THROUGH SAID ELECTROLYTE BETWEEN SAID ANODE AND SAID CATHODE TO DEPOSIT SAID ALLOY UPON SAID CATHODE, SENSING THE MAGNETIC HYSTERESIS OF SAID DEPOSITED ALLOY, CONVERTING THE SENSED MAGNETIC PROPERTY TO AN ELECTRICAL SIGNAL AND APPLYING SAID ELECTRICAL SIGNAL TO ADJUST THE VOLTAGE BETWEEN SAID ANODE AND SAID REFERENCE ELECTRODE TO PROVIDE A PRESELECTED DISTRIBUTION OF MAGNETIC PROPERTY IN SAID DEPOSITED ALLOY. 